In a telecommunications network (e.g., mobile/cellular network), user equipment (UE—e.g., mobile/cellular telephone, mobile device, etc.) establishes a communication link with a transceiver node (e.g., base station, cell site, BTS, NodeB, eNodeB, access point, access node, femto cell, pico cell). This communication link allows transmission of data from the UE to the transceiver node (uplink, UL) and, also, reception of data from the transceiver node to the UE (downlink, DL).
Standard-setting bodies within various telecommunications industries, such as ETSI, have promulgated standards for how user equipment (UE) is required to uplink (UL) and downlink (DL) to transceiver nodes. These standards require the user equipment to UL and DL with the same transceiver node. Thus, when the UE migrates out of range from one transceiver node and into range of another transceiver node, the standards require simultaneous handoff/handover or reselection of both the UL and DL from one transceiver node to another. This simultaneous transfer of both the UL and DL has some disadvantages.
Transceiver node selection in conventional cellular networks is based on the DL signal level only, where a UE in idle mode measures the received signal power from different transceiver nodes and a transceiver node selection decision is taken based on the strongest received signal power.
This approach is adequate in homogeneous networks composed of Macro transceiver nodes (e.g., MeNB). However, the introduction of heterogeneous networks (HetNets) composed of MeNBs and small transceiver nodes (e.g., SeNBs) makes the transceiver cell node selection based on the DL received power very inefficient in terms of the UL.
DL coverage is based on the transmission power of a transceiver node. SeNBs have a much smaller coverage area than MeNBs because they tend to have a much lower transmission power. However, UL coverage depends on the terminal transmission power which is more or less the same whether the terminal is transmitting to a SeNB or MeNB. This fact creates an imbalance in the UL and DL coverage in a HetNet scenario.
The imbalance problem also causes high interference scenarios where MeNB UEs cause high interference to the SeNB UEs when these MeNB UEs are very close to (or in) the coverage area of the SeNBs. This interference can more severely affect UEs engaging in Device-to-Device (D2D) communication, when the D2D connection is in band and is using the UL cellular resources (as e.g. in Rel-12 LTE D2D, which is fully incorporated herein by reference). If we have two devices communicating in a D2D fashion in a SeNB, a MeNB UE that is very close to the SeNB coverage could cause a high level of interference to the D2D couple because the interference is received at the devices and not at the SeNB/Scell as in a typical cellular connection. Also, if we assume a scenario where two devices covered by a MeNB are communicating in a D2D fashion and are located near the cell edge of a MeNB, UEs covered by a SeNB located close to the same (above-mentioned) cell edge would both perceive and inflict a high level of interference from the D2D pair. This happens because both D2D UEs and cellular UEs are power controlled in the uplink based on their pathloss to their serving eNB. When UEs are covered by the same eNB, they are scheduled in a manner so as not to cause interference at the receiving eNB. However, when they are covered by different cells that are nor synchronised or coordinated, avoiding (or mitigating) interference is not possible. As mentioned above, this issue is even more pronounced when the interference is perceived by neighbouring (e.g. D2D) UEs.
Also, cell loads in UL and DL are different in terms of volume where the DL load is generally much larger than the UL (a DL:UL ratio of 80:20 has been observed). The DL and UL volumes are not necessarily dependent, meaning that a cell or a UE having high UL traffic volume does not necessarily have high DL traffic volume too. In fact mostly the UL and DL traffic volumes are independent.
A known proposed solution to this imbalance problem is to decouple UL and DL transceiver node association, where DL transceiver node association is based on the DL received power whereas UL transceiver node association is based on path loss.
US20130163441A1 discloses decoupling downlinks and uplinks between UEs and transceiver nodes. The transceiver node for the DL connection with the UE is determined as a function of DL signal strength. The transceiver node for the UL connection with the UE is determined as a function of path loss. Determining path loss is performed by subtracting a measured signal strength at the UE from the transmit power of each transceiver node. The path loss for each transceiver node is then used as a proxy for UL signal strength, and the UL signal strength is then used as a basis for determining which transceiver node is optimal for UL from the UE. In other words, a processor within the UE determines the DL signal strength and also the received signal strength, and then calculates the path loss as a function of the DL signal strength and the received signal strength. An optimal UL transceiver node is then determined as a function of the path loss.
US20130089034A1 discloses an arrangement in which a UE can associate with different transceiver nodes for its UL and DL communications. To achieve this, the two transceiver nodes communicate with each other. A signalling methodology within a cellular standards framework (such as LTE) is disclosed, by which a UE can associate with a different transceiver node for UL and DL communications and further facilitate communication between a transceiver node handling UL and a transceiver node handling DL. The selection of a transceiver node by sending a Sounding Reference Signal (SRS), which allows a received power value to be determined, is disclosed. The applicability to heterogeneous networks, where different transceiver nodes can have different transmit powers, is discussed.
U.S. Pat. No. 8,824,326 B2 (“Method and apparatus for managing device-to-device interference”) discusses interference management for D2D by sensing interference on the resources and trying to schedule the D2D communication on resources that have a low interference level. This prior art document is in the context of a ‘traditional’ telecommunications network, i.e. the UE is connected to the same cell in UL and in DL. Accordingly, the prior art does not solve the problem of D2D interference management in a decoupled UL/DL telecommunications network.
US 20120051315 A1 (“Method and Apparatus for Managing Device-to-Device Interference”) also relates to interference and proposes to solve interference issues by scheduling D2D on resources that are less interfered. This prior art document is also in the context of a ‘traditional’ telecommunications network, i.e. the UE is connected to the same cell in UL and in DL. Accordingly, the prior art does also not solve the problem of D2D interference management in a decoupled UL/DL telecommunications network.